1. Field of the Invention
The present invention relates in general to a PC card, and more specifically to a multifunction-type PC card having a plurality of card information structures, or CISs, which constitute the functional attribute information of the PC card, and a CIS switching mechanism.
2. Description of the Related Art
Generally speaking a PC card contains circuitry for realizing its functions and a storage area for the CIS, which provides the functional attribute information of the card. Here the term "functions" is intended to refer to local area network (LAN) access, modem, memory, PHS, PDC, terminal adapter (TA), FM tuner, AM tuner, TV tuner, and the like.
FIG. 8A is a drawing showing the structure of a single-function PC card. The logic for realizing single function 1 and a single CIS corresponding to that function are contained within the PC card. When using this type of PC card, the user is required to change the PC card inserted into the PC card slot of a personal computer or the like in accordance with the purpose.
Alternatively, to avoid the inconvenience of changing PC cards, PC cards may be manufactured incorporating logic for the realization of a plurality of functions, as is shown in FIG. 8B. In this case the CIS contains functional attribute information corresponding to function 1 and function 2 respectively. When using this type of PC card, the PC must be provided with a card driver having multifunction capability, by means of which the two sets of functional attribute information resident in CIS1 are read into the personal computer memory, allowing the personal computer to recognize the two functions.
CISs are defined by rules conforming to PC card standards established by PCMCIA in the United States and by JEIDA in Japan, under which the CIS of a PC card is stored starting from the leading address of the CIS storage memory area. Further, the end of the CIS is indicated by a pre-determined delimiter.
When a multifunction-type PC card is inserted into the slot of a personal computer that does not have installed therein a driver with multifunction capability, the personal computer, in accordance with the above-cited standards, reads the CIS from the leading address of the CIS storage area up to the delimiter into the personal computer memory. The CIS corresponding to function 2, which is stored after the CIS corresponding to function 1, is not transferred to the personal computer memory. As a result, even though a multifunction-type PC card is inserted into the personal computer, the computer recognizes it as a single-function PC card having function 1.
When, on the other hand, a multifunction-type PC card is inserted into the PC card slot of a personal computer in which a driver with multifunction capability is installed, the computer reads in the plurality of CISs and activates the corresponding functions. That is to say, all the functions resident in the PC card inserted in the slot are activated, irrespective of whether they are actually used or not. This results in unnecessary consumption of power. Reducing power consumption is of particular importance in the case of battery-operated information equipment.
Let us consider an example of a PC card 1 having two functions: a modem and an ATA memory. The modem draws a current of approximately 120 mA and the ATA memory draws approximately 1 mA in standby mode. In common types of cards, the frequency of use of the ATA memory is higher than that of the modem. It is sufficient if the modem is activated only during the exchange of data with external systems. Nevertheless the PC card draws 121 mA of current at all times.
CIS switching mechanisms are also described in co-pending U.S. patent application Ser. Nos. 08/984,232 and 08/984,597, filed on even date herewith.